Measuring impurity concentrations accurately is very important in the development and manufacture of semiconductor devices. As an example, a bipolar junction transistor (BJT) is used for amplifiers of high frequency signals because it is capable of low noise and high-speed operation. For example, in a BJT in which a base layer and an emitter layer are formed by epitaxial growth, by thinning the base layer to a thickness of 100 nm or less, the minimum noise figure can be reduced and high-speed operation can be exhibited in the gigahertz range.
In an npn BJT, Boron, for example, is introduced into the base layer as a p-type impurity. As the boron concentration in the base layer increases, the base resistance decreases to reduce the current gain. On the other hand, although the base resistance increases, the current gain is improved as the boron concentration decreases. Hence, the boron concentration in the base layer is optimized based on the use of the BJT.
In addition, SiGe, which is silicon (Si) compound containing Germanium (Ge), may be used for the base layer. By increasing the Ge concentration gradually from the emitter side to the collector side, an electric field direct from the collector to the emitter can be induced in the base layer. Thereby, the response speed of the BJT can be increased.
Thus, the BJT requires controlling the concentration of a p-type impurity introduced into the base layer accurately. Furthermore, since the electric field induced in the base layer depends on the concentration gradient of Ge, the control of the concentration profile of Ge is important. However, it is difficult to directly measure the concentration of a p-type impurity and the concentration profile of Ge in a base region of a microfabricated BJT. This creates a need for a method for measuring an impurity concentration profile that enables accurate control of the impurity concentration and the concentration profile of Ge in the base layer of the BJT and a method for manufacturing a semiconductor device using the measuring method, for example.